The production of water-containing cement preparations or concrete is attended by the problem of keeping the viscosity of the mix so low during production, transportation and use that problem-free processing is possible without the mixture becoming so thinly liquid that it runs from the mold. This equilibrium can be established through the water content, although such a quantity would generally be required that the cure time would be greatly increased. For this reason, viscosity adjusters are added to the preparations to keep the viscosity in the necessary range, even without the addition of relatively large quantities of water, and at the same time to delay the open time or setting time to such an extent that curing does not occur in transit.
Various polymers and their use as cement or concrete plasticizers are known from the prior art. EP 1090901 A1 (Takemoto) describes a process for the production of polyether esters with average molecular weights in the range from 5,000 to 40,000, in which methoxy polyalkylene glycol ethers are first reacted with methacrylic acid and the monomers obtained are polymerized in aqueous solution. U.S. Pat. No. 5,614,017 and U.S. Pat. No. 5,670,578 (Arco) both describe polymers obtained by esterification of polycarboxylic acids with polyethers. The reaction takes place in two steps, the mixture first being heated to 120° C. to remove water and then to 170° C. in order to carry out the actual esterification. According to U.S. Pat. No. 6,034,208 (Arco), hydroxy (meth)acrylates are reacted with alkylene oxides and the adducts obtained are polymerized with acrylic acid. U.S. Pat. No. 5,919,300 (Sika) discloses copolymers obtained by copolymerization of (a) N-vinyl amides or lactams, (b) esters of methacrylic acid with polyethylene glycols and (c) methacrylsulfonic acid. U.S. Pat. No. 5,665,158 (Grace) describes polymers obtained by reaction of poly(meth)acrylic acid with alkoxylated amines. The teachings of U.S. Pat. No. 6,139,623 and U.S. Pat. No. 6,172,147 (Grace) add to this process to the extent that defoamers (tributyl phosphate) or anionic surfactants (alkyl ether sulfate) are added in a final step.
Unfortunately, the known additives are far from satisfactory in regard to their performance properties. In many cases, viscosity is not sufficiently reduced so that the mixes solidify in transit from the manufacturer to the building site and can only be processed with considerable difficulty. Although, in other cases, viscosity is sufficiently reduced, the effect is time-dependent, i.e. either there is a complete collapse of viscosity or the mix suddenly solidifies—neither of which is, of course, desirable.
Accordingly, the problem addressed by the present invention was to provide new polymeric additives for the production of water-containing cement preparations or concrete, so-called “superplasticizers”, which would be free from the disadvantages mentioned at the beginning and, in particular, would have better viscosity-adjusting properties.